Difficulty in rising from a chair is common in older adults and is associated with an increased risk for falls. Compared to standard functional assessment techniques, we will use a more quantitative approach. This approach will: improve the assessment of both mild to moderate dysfunction and changing functional status; help clarify relationships among aging, impairment, and disability; and be useful in the design of more effective interventions. The overall objectives of Project 3 are to quantify the effects of age, functional disability, and the presence of Parkinson's disease on chair rise biomechanics. Subjects will be recruited based on their chair rise performance in Project 1 (Lo-tech Tasks), to perform similar chair rise tasks as part of the Hi-tech Analyses of Lo-tech tasks. In the second part of Project 3, the Hi-tech Tasks, a separate subject group will be recruited to perform a series of Ordered Chair Rise Tasks. Designed to vary substantially in difficulty, the Ordered Chair Rise Tasks consist of controlled rises under conditions that differ in hand and foot support, seat height, and rise speed. As another part of the other Hi-tech Tasks, a healthy older adult group will perform a series of Unordered Chair Rise Tasks, designed to examine the contribution of sagittal asymmetry to rising from a chair. We will measure subject anthropometry, body segment kinematics and external support reactions. Using a biomechanical model, these data will be used to conduct inverse dynamics analyses that will provide the peak joint torque strengths used. We will compare joint motions and joint torques used in the chair mobility tasks with clinical measures of joint range of motion and muscular strength available. Finally, we will examine the relationships among chair rise task success, the joint ranges of motion and torque strengths used when they succeed, and: (1) physical abilities such as joint strength; and (2) neuropsychological measures such as fear of failing. Understanding how rising from a chair is affected by aging, neuropsychological status, and physical impairment will likely improve assessment and intervention. A biomechanical analysis of different task conditions can demonstrate the relationship between required joint range of motion and strength and conditions leading to successful rising from a chair. Finally, deficits in Parkinson's disease fit well with our paradigm of studying the effect of neuropsychological and physical components on the biomechanical parameters of mobility.